What produces this noise?? (early group B rally car vid)
12-15-2007, 06:17 AM
#1
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What produces this noise?? (early group B rally car vid)
I recall maybe Fusiliers car does the same thing..
It sounds kinda like a blow off valve?<ul><li><a href="http://www.youtube.com/watch?v=iKyLxxM41Zw&NR=1">http://www.youtube.com/watch?v=iKyLxxM41Zw&NR=1</a</li></ul>
It sounds kinda like a blow off valve?<ul><li><a href="http://www.youtube.com/watch?v=iKyLxxM41Zw&NR=1">http://www.youtube.com/watch?v=iKyLxxM41Zw&NR=1</a</li></ul>
12-15-2007, 07:52 AM
#2
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Re: What produces this noise?? (early group B rally car vid)
Dump valve. Valve limiting pressure in intake manifold. Turbo bypass valve can make similar noise if is unloading to atmosphere.
12-15-2007, 09:05 AM
#4
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That is the sound of pressure backing up on the turbo compressor.
The race cars had no bypass or blow-off valves. You can't hear that sound on a normal ur quattro because of the plumbing and air filter.
FWIW, that car is a replica as you can see from stock shifter, pedals, etc.. There is other footage of it floating around showing the engine, which is a mildly tweaked 20Vt. From the sound, you can tell that it doesn't have really aggressive cams.
FWIW, that car is a replica as you can see from stock shifter, pedals, etc.. There is other footage of it floating around showing the engine, which is a mildly tweaked 20Vt. From the sound, you can tell that it doesn't have really aggressive cams.
12-16-2007, 10:30 AM
#6
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Re: That is the sound of pressure backing up on the turbo compressor.
I was wondering about that car as they show the hood up in the end, and they are looking upon a 20...
I initially thought it was a bad editing job, and they were looking at different car.
I initially thought it was a bad editing job, and they were looking at different car.
12-16-2007, 05:13 PM
#7
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Don't know if that one
had a BOV or BPV, but you can hear a BPV. Mine has one and you can hear 'it' because even though it's bypassing, there is so much pressure and the way it's plumbed it still vents some through the WG and the whole system makes that sound.
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12-17-2007, 10:34 AM
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Its compressor surge. 100% positive
Not the Wastegate, not the BPV, not the BOV not the Dump Valve. The sound is made only when the car shifts and not at WOT when the Wastegate opens. BOV is more of a Whoosh sound. Gary's Ersatz S1E2 has a BOV which makes a Whoosh. BPVs are pretty quiet.
Why didn't Audi use a BOV or BPV on their cars?. They did exist in the last 90s and the SQ was fitted with one. (one of the first cars to have one IIRC). They ran the I5 up to the IMSA without either a BPV or a BOV. Basically the story I got from Lehmann and the Sprongls is that the Recovery time after the BPV opened and until the car got back on boost was not working for the drivers. Boost is actually lost until the turbo can overcome the leak which is the BPV and get the intake manifold back into boost pressure range which then closes the BPV. So the larger BPV you use to dump the pressure, the bigger the leak and more laggy the response is. The turbo is definately not stressed as much with the BPV or BOV.
The R10 doesn't have throttle bodies so if you listen closely you can hear its turbos surging a bit when it comes off-throttle going into a corner. It sounds a bit like a whisp whisp whisp. Of course the intake boost spike will open up the WG in the case of an R10 which means the engine isn't pushing the turbo to surge, but the inertia of the turbo will still cause some surging.
Why didn't Audi use a BOV or BPV on their cars?. They did exist in the last 90s and the SQ was fitted with one. (one of the first cars to have one IIRC). They ran the I5 up to the IMSA without either a BPV or a BOV. Basically the story I got from Lehmann and the Sprongls is that the Recovery time after the BPV opened and until the car got back on boost was not working for the drivers. Boost is actually lost until the turbo can overcome the leak which is the BPV and get the intake manifold back into boost pressure range which then closes the BPV. So the larger BPV you use to dump the pressure, the bigger the leak and more laggy the response is. The turbo is definately not stressed as much with the BPV or BOV.
The R10 doesn't have throttle bodies so if you listen closely you can hear its turbos surging a bit when it comes off-throttle going into a corner. It sounds a bit like a whisp whisp whisp. Of course the intake boost spike will open up the WG in the case of an R10 which means the engine isn't pushing the turbo to surge, but the inertia of the turbo will still cause some surging.
12-17-2007, 10:43 AM
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You have to remove the CIS.
Off throttle, throttle body and airplate closes so you can't hear the surging on an urquattro. Airplate, airbox and airfilter all obstruct the sound. Its there though.
Pierburg 10V Rally cars used a series of cables to connect the fuel distributor(which was by the driverside firewall) to the throttle body. Alot like airplane control linkages. So there was no Airplate to hide the sound, also the intake air pipe which fed the turbo even had a trumpet shaped thingy to bark the sound out to relieve pressure which kept the intake from blowing off.
Bosch EFI 10V cars had the same setup.
Bosch EFI20V cars used the same intake as the 10V cars.
S1's used an airbox mounted right to the turbo so they were very loud.
The heavier and larger the turbo the more loud it is. Also the more boost you run the more loud it is. Hence the IMSA is extremely loud.
nearly 2 bar of boost and a K27#13 hotside housing with a K29 compressor.
Obviously the heavy K26 in the urquattro can take the beating. I would think an RS2 can do it. K27s can take the beating and last you 3-4K miles of 100% on power beating. The Authentic S1 Sound is main reason I went with a K27/K29 turbo over a Garrett BB turbo.
Pierburg 10V Rally cars used a series of cables to connect the fuel distributor(which was by the driverside firewall) to the throttle body. Alot like airplane control linkages. So there was no Airplate to hide the sound, also the intake air pipe which fed the turbo even had a trumpet shaped thingy to bark the sound out to relieve pressure which kept the intake from blowing off.
Bosch EFI 10V cars had the same setup.
Bosch EFI20V cars used the same intake as the 10V cars.
S1's used an airbox mounted right to the turbo so they were very loud.
The heavier and larger the turbo the more loud it is. Also the more boost you run the more loud it is. Hence the IMSA is extremely loud.
nearly 2 bar of boost and a K27#13 hotside housing with a K29 compressor.
Obviously the heavy K26 in the urquattro can take the beating. I would think an RS2 can do it. K27s can take the beating and last you 3-4K miles of 100% on power beating. The Authentic S1 Sound is main reason I went with a K27/K29 turbo over a Garrett BB turbo.
12-17-2007, 10:48 AM
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its nearly impossible to hear compressor surge from inside the car when at WOT and shifting rapidly.
Outside its louder than the engine and can be heard from a great distance. I think its because the sound is from the turbo right out the front of the car like a loudspeaker, whereas a BOV is inside the engine bay.
Strangly, I've heard BPV sounds from inside a car. I've heard BOV sounds from outside and inside a car. But I've not heard BPV sounds from outside a car.
Strangly, I've heard BPV sounds from inside a car. I've heard BOV sounds from outside and inside a car. But I've not heard BPV sounds from outside a car.